The invention concerns a method for the operation of freeze-drying equipment with a chamber and with loading and unloading devices, including equipment appropriately designed for such purpose having the characteristics of the superimposed concepts of the independent patent claims.
In modern freeze-drying equipment, as known from U.S. Pat. No. 5,129,162, U.S. Pat. No. 5,649,800 and DE 103 07 571 A1, there exists the necessity of charging a multitude of charging areas, which are arranged on top of each other in a chamber with a multitude of containers, small bottles and similar items and to remove same again from the charging areas after completion of the freeze-drying process.
The containers come from a filling device via a conveyor belt to the freeze-drying chamber. Customarily, the filling device essentially operates on a continuous basis; whereas, the loading of the charging areas takes places intermittently. It is therefore necessary to provide a buffer zone for the containers between the filling device and the chamber. It consists, for example, of a multitude of conveyor belt loops adapted to the buffer demand.
Loading of the chamber or of the charging areas takes place with the aid of a transfer table and a slider system, namely through a lockable loading aperture which is part of a wall or a door of the freeze-drying chamber. In its operating position, the transfer table connects the planes of conveyor belt and charging area to be loaded.
In the feed and loading phases, the containers are still open. Traditionally, a cork, which has a cut-out for the evacuation of the water vapor during freeze-drying, is positioned on the opening of the containers. After completion of the freeze-drying process, the closing of the corks takes place in the still locked chamber by driving the charging areas together. After opening of the loading aperture follows the unloading of the charging areas, which likewise takes place with the aid of the transfer table and the slider system. With the aid of the already mentioned or via an additional conveyor belt, the containers are brought to a device where they are fitted with caps.
Freeze-drying predominantly serves for conservation of pharmaceutical products so requirements in regard to sterility are very high. Freeze-drying installations therefore are located in clean-rooms or they are equipped with so-called isolators. The isolator room, which is preferably constituted by transparent wall sections, encloses those areas of the freeze-drying equipment in which clean-room conditions must be maintained. This includes mainly the means, in particular conveyor belts, which serve for taking the still open containers from the filling device up to the chamber and the area before the chamber in which the loading and unloading means are arranged. Generally, the transport means between the freeze-drying chamber and the device for final sealing of the containers with caps are also arranged in the isolator.
With increasing number of containers of product to be freeze-dried, the loading times become longer and longer. Frequently it is no longer possible to load the up to 2 square meter or larger charging areas in one single push. A multitude of partial pushes is needed. Each partial push requires a “to and fro” movement of the loading slider. Loading time and charging plate changing time becomes significant longer as a result. In addition, the need arises to enlarge the buffer zone.
The products to be freeze-dried are, as a rule, more or less temperature-sensitive. The charging areas or plates are therefore already during the loading phase adjusted to low temperatures (for example minus 20° C.). In order to avoid loss of quality in the end product, the goal is to also have at the start of the freeze-drying process a temperature as uniform as possible in the majority of containers. It is, therefore, the objective to keep the heat exchange as low as possible between the interior of the chamber and/or the interior of the isolator room. This is done, on the one hand, by selecting the smallest possible loading aperture. It extends across the width of the chamber and has a height which is only a little larger than the height of the loading means (transfer table, slider system). If the temperature sensitivity of the product is particularly high, it is, in addition, necessary to close the loading aperture between each of the loading pushes or partial pushes.
This requires that the transfer table which connects the planes of the conveyor belt and the charging area to be loaded, is driven in before each push and driven out after each push. Opening and closing times of the loading aperture as well as the time required for constant in and out movement of the transfer table significantly extend the loading time. The buffer zone, along with the corresponding isolator rooms, must be expanded according to the extended loading times.